Retrieval of THotkey failed. Error code 0x00031402

Running WindowsXP toshiba notebook, (tecra M7-s7331). Notebook boots-up OK, and soon after an error comes up as follows:TouchEd Error. Retrieval of THotkey failed. Error code 0x00031402, 0x00000002. Everything is working OK on computer except can no longer use the Fn key to turn down the brightness on the screen or any other Fn functions.I tried a few options that I found on the web.